fix: factory array default value

[muktihari]

The changes:

• Previously in the factory on RecordMesg, compressed_speed_distance's Value was uint8(255), this is not correct since the field is an array [3]uint8 field, now it is changed to []uint8(nil). This validator will handle this gracefully, while it is nil value but not a nil type so validator will not complain, and since it is a nil value, nothing will be written to the file on encoding process (marshal).
• We use slice as it is convenient to work with slices and for simplicity, it's user responsibility to validate the size of the slice, for the example above, it should match len 3. We encourage user to write a good code rather than having bunch of validators to validate all possibilities, we will provide verbose comment in our type declaration for helping user writing the good code.

Notes:

• This update should not change the current behaviour in our SDK.
• Users are less likely to be affected and if it does, it should be a minor.
• This update give us more proper array handling.